Lower Left Back Pain: Causes and When to Worry

Lower left back pain can feel like a deep ache just above the left buttock, a sore spot beside the spine, or a sharp catch when you bend or turn. In most cases it comes from the muscles, joints or discs of the lower back and settles over a few weeks with the right kind of movement.

The left side of the body has its own set of nearby organs, including the left kidney, the lower part of the large bowel and, in women, the left ovary. This guide explains how to tell back pain from pain that may be coming from elsewhere, the warning signs to act on, and what helps.

Quick answer

Lower left back pain is most often caused by a strained muscle, an irritated joint or a disc problem, frequently after lifting, twisting, sport or sitting for long periods. It usually improves within a few weeks with gentle activity. Less often, it comes from the left kidney, the bowel (such as diverticulitis), period pain or endometriosis. Call 999 for sudden, severe back or tummy pain with fainting, and seek urgent help for back pain with fever, pain when peeing or blood in your poo.

Why does the lower left side of my back hurt?

When the lower left side of your back hurts, the most likely explanation is mechanical: something in the back itself has been overloaded or irritated. Common triggers include:

• Lifting something heavy or awkward, especially with a twist to the left
• Repeated bending, such as gardening or DIY
• Carrying a heavy bag on the left shoulder, or a child on the left hip
• Driving or desk work with the body turned slightly to one side
• Running or walking with a limp from an ankle, knee or hip problem on one side

Pain that changes with posture and movement, eases with gentle activity and feels tender over the muscles is very likely to be coming from the back. Our guide to what causes back pain explains the general causes in more detail.

Muscular and spinal causes of lower left back pain

Left side back strain

A left side back strain affects the muscles and ligaments beside the lower spine. It often causes an aching pain in the lower left back with tightness or spasm, pain when bending forward or straightening up, and stiffness after rest that eases as you move.

Left lower lumbar back pain from the joints

The lumbar spine has small facet joints on each side. Irritation on the left can cause a well-defined ache that is worse when you arch backwards, turn to the left or stand still for a long time, and better when you sit or bend forward slightly.

Sacroiliac joint and pelvic pain

Pain from the left sacroiliac joint is felt very low, in the bottom left of the back or the dimple above the buttock. It can be aggravated by stairs, getting in and out of a car, or standing on one leg, and is common during and after pregnancy.

Disc problems and sciatica

A disc that bulges to the left can irritate a nerve root and cause pain, tingling or numbness spreading into the left buttock and leg. Leg pain that is worse than the back pain is a typical sign of sciatica, and a slipped disc is one of its most common causes.

Hip problems

Problems in the left hip, such as osteoarthritis or irritation of the tendons on the outside of the hip, can cause pain in the buttock and lower back as well as the groin or thigh. Stiffness when putting on socks or pain lying on that side are clues.

Lower left back pain from organs

Organ-related causes are less common, but the pattern of symptoms can help. Pain that does not change when you move, wave-like pain, and symptoms such as fever, sickness, or changes in your urine or bowels point away from the back.

Left kidney: stones and infection

• Kidney stones: severe pain in the left side and back, below the ribs, that comes in waves and may spread to the groin, often with restlessness, sickness and blood in the urine.
• Kidney infection: back or side pain with a high temperature, shivering and burning when peeing.

Bowel causes, including diverticulitis

Diverticula are small pouches in the wall of the large bowel, most often in the lower left part. When they become inflamed or infected (diverticulitis), they cause pain in the lower left of the tummy, which some people also feel in the back, along with a high temperature, feeling sick and changes in bowel habit. Constipation and trapped wind can also cause a dull ache felt on the left side of the back. Inflammatory bowel disease is another cause of tummy pain and changes in bowel habit that needs GP assessment.

Abdominal aortic aneurysm

The aorta, the main blood vessel from the heart, runs down the back of the abdomen slightly to the left of the spine. An abdominal aortic aneurysm is a swelling in its wall. It usually causes no symptoms, but if it leaks or bursts it causes sudden, severe pain in the tummy or lower back, often with dizziness, sweating or fainting. This is a medical emergency. Men aged 65 and over, smokers and people with high blood pressure are at higher risk.

Lower left side back pain in females

As well as the usual muscle and joint causes, lower left side back pain in women can be linked to:

• Period pain: cramping pain in the lower tummy that often spreads to the lower back and thighs, starting around the time of a period. Our guide on how to stop period pain fast covers what helps.
• Endometriosis: tissue similar to the womb lining grows elsewhere, causing period pain that stops you doing normal activities, pain during or after sex, pain when going to the toilet, and sometimes back pain. It is worth seeing a GP if you recognise these symptoms.
• Ovarian cysts: sometimes cause a dull ache on one side. Sudden severe pain may mean a burst cyst or a twisted ovary and needs A&E.
• Pregnancy: lower back and pelvic girdle pain are common and usually respond to exercise and advice. Pain with bleeding in early pregnancy needs urgent assessment.

When to worry about lower left back pain

Call 999 if you have:

• Sudden, severe pain in the back or tummy with dizziness, sweating, a racing heart or fainting
• Numbness around the genitals or bottom, new difficulty peeing, or loss of bladder or bowel control
• Numbness or weakness in both legs

Go to A&E or get same-day help from NHS 111 if you have:

• Severe pain in the side or back that comes in waves, or blood in your urine
• Back pain with a high temperature, shivering and pain when peeing
• Pain in the lower left of the tummy with a high temperature, vomiting or blood in your poo
• Sudden severe pelvic pain, or one-sided pain with bleeding if you could be pregnant

See your GP if:

• The pain has not started to improve after a few weeks
• You have a change in bowel habit, unexplained weight loss or have had cancer before
• Painful periods are affecting your daily life
• Leg pain, numbness or weakness is spreading or getting worse

Lower left back pain relief: what helps

• Keep moving: short, regular walks and normal daily activity usually help recovery more than rest.
• Heat: a heat pack or warm bath can relax tight muscles.
• Painkillers: anti-inflammatory painkillers such as ibuprofen may help if they are suitable for you. Ask a pharmacist if unsure.
• Sleep position: try lying on your side with a pillow between your knees, or on your back with a pillow under your knees.
• Swap sides: change which shoulder you carry bags on and which way you turn when lifting.
• Exercise: start with gentle knee rolls, pelvic tilts and walking, then build up. Our lower back pain exercises show eight moves step by step.

How a physiotherapist helps

A physiotherapist will listen to how the pain started, screen for warning signs, and assess your spine, pelvis and hips. Treatment usually includes:

• A graded exercise programme to restore movement and build strength
• Hands-on treatment alongside exercise to ease pain and stiffness
• Practical advice on sitting, lifting, sleep and staying active at work
• Referral to your GP if symptoms suggest a cause outside the back

This approach is in line with NICE guidance, which places exercise at the centre of care for low back pain.

Frequently asked questions

Is lower left back pain serious?

Usually not. Most cases are muscular and improve within a few weeks. Get prompt help if it comes with fever, urinary symptoms, bowel changes or sudden severe pain.

Can constipation cause lower left back pain?

It can cause a dull ache low on the left, as the last part of the bowel sits on that side. It should ease as constipation settles. See a GP if bowel habits change for no clear reason.

What causes lower left back pain in women?

Muscle strain is still the most common cause, but period pain, endometriosis, ovarian cysts and pregnancy can also cause pain in the lower left back.

How do I know if lower left back pain is my kidney?

Kidney pain is usually higher, just below the ribs, comes with fever or pain when peeing, and does not change much with movement.

Why does my back on the left side hurt when I bend?

Pain on bending usually comes from strained muscles, irritated joints or a disc. It often improves with gentle movement and exercise over a few weeks.

Lower back pain treatment in Chiswick

Lower left back pain is assessed and treated at Omnia Lifestyle, 8 to 9 Bedford Corner, The Avenue, Chiswick W4 1LZ, close to Turnham Green station, on bus routes 94, E3 and 272. Limited parking is available on request when booking. Assessment checks for warning signs, pinpoints whether the pain is coming from the back and builds a plan of exercise and hands-on treatment.

Read more about back pain, sciatica and slipped discs, explore physiotherapy, or book an assessment.

This article is general information, not medical advice. If you have any of the warning signs listed above, seek medical attention.